New finds of Merck rhinoceros (Stephanorhinus kirchbergensis jager 1839) (Rhinocerotidae, mammalia) in Ob area, Tomsk region

The remains of Merck rhinoceros (Stephanorhinus kirchbergensis Jager 1839) are rare in Ob area. The finds in Tomsk region originate from both already known location - Krasniy Yar, and two new ones - Asino and Kindal. A finding of a tooth in the south of the Krasnoyarsk Territory is a first find for the region, and is extremely important in linking spatially the rhino distribution in Western and Eastern Siberia. The most important finding is a lower jaw found in the mouth of the ducts Kindal in the left bank of the river Ob, down river from Kar-gasok at a depth of about 14 m below water level. Site is located 400 kilometers to the north from the city of Tomsk (59°08 'N, 80°35' E). As of now, this is the first find of the mandible S. kirchbergensis in Western Siberia. The finding at Kindal Location is the most northern site for Western Siberia where S. kirchbergensis was found, and is closer to the finding at Viluy River in Yakutia (63°40 'N) by a latitudinal position. The geological age of the new discoveries is the beginning of the Middle Neopleistocene (Tobolsk horizon; MIS 9-11). The lower jaw belongs to an adult animal with preserved teeth p3-m3. Teeth are with the high crowns. The tooth m3 is in the initial stage of dental abrasion. Teeth are large, especially the m1, their sizes are similar to the ones of large specimens of Moldavia, the Volga region and Taubah, but smaller than the teeth of specimens from Krasniy Yar. The molars m1-3 (171 mm) are longer than the ones of European samples. The closest in length of these teeth is a large specimen from Taubah (157,8-169,9 mm). Merck rhinoceros are considered as a final stage/section in the phylogenetic line of S. megarhinus - S. kirchbergensis. Comparative analysis of main measurements of lower jaws, which are considered to be S. kirchbergensis from Eurasian locations, proved how different they are from S. ex gr. megarhinus-kirchbergensis from Haprov layers; there is no even overlapping in limit/boundary values. The lower jaw of rhinoceros is significantly smaller than S. kirchbergensis. However, comparing it with S. megarhinus is much more difficult and not as obvious. Dimensional characteristics of the lower jaws of the rhinoceros presented by C. Guerin (1980) vary within a very wide range. Upper values for some measurements are above average for S. kirchbergensis, whereas lower values falls below lower limits of S. ex gr. megarhinus-kirchbergensis. Nevertheless, average of all measurements of the lower jaw S. megarhinus is under lower values of S. kirchbergensis. Very good repeatability of the curves on the graphs can reflect similarity in relative characteristics of lower jaws of rhinoceroses and confirm their phylogenetic relationship.

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